<template>
  <ul class="list">
    <li class="item" 
        v-for="item in letters" 
        :key="item"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick">{{item}}</li>
  </ul>
</template>

<script>
export default {
  data(){
    return{
      touchStatus:false,//默认手指未触摸
      startY:0,
      timer:null
    }
  },
  updated(){
    this.startY=this.$refs['A'][0].offsetTop
  },
  props:{
    cities:Object,
  },
  computed:{
    letters(){//创建一个包含所有字母的数组
      const letters=[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
  methods:{
    handleLetterClick(e){//获取点击的字母，并传递
      var alphabet=e.target.innerText
    //  console.log(e.target.innerText)
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus=true
    },
    handleTouchMove(e){
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer=setTimeout(()=>{
          const touchY=e.touches[0].clientY-79
          const index=Math.floor((touchY-this.startY)/20)
          if (index>= 0 && index<this.letters.length) {
            this.$emit('change',this.letters[index])
          }
        },16)
        
      }
    },
    handleTouchEnd(){
      this.touchStatus=false
    }
 }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display :flex;
    flex-direction :column;
    justify-content :center;
    position :absolute;
    top:1.78rem;
    right:0;
    bottom :0;
    width :0.4rem;
    .item
      line-height :0.4rem;
      text-align :center;
      color:$bgColor;
</style>
